This invention relates to the field of high accuracy, closed loop position controlling apparatus.
In the study of burn phenomena of solid rocket propellant or grain, an interesting conflict between grain burning characteristics and photography physics is encountered. This conflict arises from the relatively small depth of field inherent in the optics of a desirable photographic system in comparison with the particle sizes occurring in state-of-the-art solid rocket propellant grain. Particle sizes in the range of 400 micrometers are, for example, to be expected in propellant grain before and during burning, while the photographic system used for recording grain burn events can be limited to depth of field characteristics as low as of 20 micrometers. Additionally since the burn rate of such solid propellant grain is in the order of 0.02 meters/second, or 20,000 micrometers per second it is clear that an in-focus view of a burning propellant grain surface over several seconds of time requires constant attention to positioning the burning surface within the camera optics depth of field. A high-resolution tracking capability linking the burn receding grain surface and advancement of the grain body is, in fact, desirable for this linking. Such capability is provided by the apparatus of the instant invention.
The patent art includes several examples of apparatus related to differing aspects of the present invention. Included in this art is the patent of Bernard G. Bricks, U.S. Pat. No. 4,442,523, which concerns a high-powered metal vapor laser such as a lead vapor laser or copper vapor laser. Also included in this art is the patent of Hans Joerg Pfleiderer et al, U.S. Pat. No. 4,496,980, which teaches a semiconductor image sensor apparatus concerned with signal integration. Further included in this art is the patent of Joseph Maserjian, U.S. Pat. No. 4,531,143, relating to a semiconductor device actuatable by the output energy of a laser.
Another patent of this art issued to L. H. Caveny, as U.S. Pat. No. 3,392,524, and concerns a burn rate sensor for a solid propellant rocket motor. The Caveny rocket motor employs burn rate sensing and controlling tubes and electrical resistance variations in order to control the burn surface area and the burn rate of the rocket motor. Additionally, the patent of F. E. Tuttle et al. U.S. Pat. No. 2,659,264, concerns an arrangement for determining velocity and acceleration characteristics of moving objects through the use of photographic images containing the moving object and a uniformly lined screen pattern and a superimposed second lined screen.
The patent art also includes the patent of T. O. Paine, U.S. Pat. No. 3,587,424, which concerns a laser camera and diffusion filter combination. The Paine aparatus employs a high-speed camera that utilizes the rotating reflector mirror principle and also employs a kerr cell for commencing and terminating the laser operation in accordance with the Q-spoiling operating mode.
The patent art also includes the patent of W. E. Buck et al, U.S. Pat. No. 3,366,439, which concerns a laser illumination and shuttering arrangement for high-speed photography. In the Buck et al patent, an argon gas pulsed laser is used in conjunction with a rotating mirror and a slitted stop plate for illuminating and photographing workpiece objects. The slitted stop plate in the Buck et al invention provides improved rise and fall times for the workpiece illumination. The Buck et al apparatus also contemplates photographic recording of a self-luminous event and employs monochromatic laser illumination with filters for suppressing the non-laser illumination.
While these examples of the patent art indicate considerable inventive activity in the high-speed photography art, none of these prior patents suggest the combination of elements and the precise rocket propellant workpiece sample positioning achieved in the present invention.